Many had wondered if the soccer superstar could reach 300 million like Beast, given his wild numbers in just a few days of launching his channel -- but Paul told TMZ Sports on Friday, he just doesn't see it happening.

Now, that's not any kind of shade from the boxer -- Paul actually praised Ronaldo for scoring the number -- but he just thinks MrBeast's digits are in a whole 'nother stratosphere.

"Kudos to him," Paul said of Ronaldo. "Hopefully he drops some awesome videos and I think it's dope that he's on the platform."

Of course, Paul knows a thing or two about how YouTube works ... he spent most of his life chasing followers on the site -- and currently has around 20 million subs.

And, while Ronaldo's numbers keep growing by the minute -- he's up over 39 mil now -- Paul says he's expecting a plateau soon.

Ronaldo likely won't care too much, after all, he's got the leg up on Beast on Instagram -- coming in with a staggering 637 million followers there.